Solar cells may be defined as devices to convert light energy into electric energy by using a photovoltaic effect of generating electrons when light is incident onto a P—N junction diode. The solar cell may be classified into a silicon solar cell, a compound semiconductor solar cell mainly including a group I-III-VI compound or a group III-V compound, a dye-sensitized solar cell, and an organic solar cell according to materials constituting the junction diode.
The minimum unit of the solar cell is a cell. In general, one cell generates a very small voltage of about 0.5V to about 0.6V. Therefore, a panel-shape structure of connecting a plurality of cells to each other in series on a substrate to generate voltages in a range of several voltages to several hundreds of voltages is referred to as a module, and a structure having several modules installed in a frame is referred to as a solar cell apparatus.
Typically, the solar cell apparatus has a structure of glass/filling material (ethylene vinyl acetate, EVA)/solar cell module/filling material (EVA)/surface material (back sheet).
In general, the glass includes low-iron tempered glass. The glass must represent high light transmittance and be treated to reduce the surface reflection loss of incident light.
The EVA used as the filling material is interposed between the front/rear side of the solar cell and the back sheet to protect a fragile solar cell device. When the EVA is exposed to UV light for a long time, the EVA may be discolored, and the moisture proof performance of the EVA may be degraded. Accordingly, when the module is fabricated, it is important to select a process suitable for the characteristic of the EVA sheet so that the life span of the module can be increased, and the reliability of the module can be ensured. The back sheet is placed on a rear side of the solar cell module. The back sheet must represent superior adhesive strength between layers, must be easily handled, and must protect the solar cell device from an external environment by preventing moisture from being infiltrated into the rear side of the solar cell module.
In general, a substrate used for the solar cell apparatus mainly includes a plastic substrate or a metallic substrate. However, when the above substrates are bent due to external physical force, the substrates may be cracked to cause damage to the light absorbing layer. In addition, the filling material used in the conventional solar cell apparatus may not have a thickness sufficient to absorb external shock due to the structure characteristic thereof.